Virtual machine migration

ABSTRACT

According to an example, virtual machine (VM) migration may include generating a redundant tunnel between a common edge device (ED) of a plurality of common EDs of a multi-site network (MSN) and a gateway ED of the MSN. A gateway media access control (MAC) address and a static route may be configured for forwarding an Internet protocol (IP) message between the common ED and the gateway ED using the redundant tunnel.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage filing under 35 U.S.C 371 of PCTapplication number PCT/CN2014/075171, having an international filingdate of Apr. 11, 2014, which claims priority to Chinese PatentApplication No. 201310132255.9 filed Apr. 16, 2013, the disclosures ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND

A multi-site network (MSN) typically includes a core network that may bea public network and a site network that may be a private network. Thesite network typically includes an edge network and an access network,and is connected to the core network through the edge network. The edgenetwork is typically designated as the network between a convergencedevice and an edge device, and the access network is typicallydesignated as the network between an access device and the convergencedevice. The MSN also includes an overlay network that is a virtualnetwork created between edge devices of site networks for providing aLayer 2 interconnection between the site networks. The MSN may be usedto connect multiple geographically dispersed data centers to share load.

BRIEF DESCRIPTION OF DRAWINGS

Features of the present disclosure are illustrated by way of example andnot limited in the following figure(s), in which like numerals indicatelike elements, in which:

FIG. 1 illustrates a MSN including a VM migration apparatus, accordingto an example of the present disclosure;

FIG. 2 illustrates further details of the VM migration apparatus of FIG.1, according to an example of the present disclosure;

FIG. 3 illustrates the MSN of FIG. 1, illustrating migration of a VM,according to an example of the present disclosure;

FIG. 4 illustrates a method for VM migration, according to an example ofthe present disclosure;

FIG. 5 illustrates further details of the method for VM migration,according to an example of the present disclosure; and

FIG. 6 illustrates a computer system, according to an example of thepresent disclosure.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to examples. In the following description,numerous specific details are set forth in order to provide a thoroughunderstanding of the present disclosure. It will be readily apparenthowever, that the present disclosure may be practiced without limitationto these specific details. In other instances, some methods andstructures have not been described in detail so as not to unnecessarilyobscure the present disclosure.

Throughout the present disclosure, the terms “a” and “an” are intendedto denote at least one of a particular element. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on.

Examples of a VM migration apparatus and a method for VM migration aredisclosed herein for implementing migration of VMs, for example, in aMSN. A MSN may include a plurality of geographically dispersed networksites, e.g., local area networks (LANs), that are interconnected by awide area network (WAN), such that the plurality of geographicallydispersed network sites together act similarly to a single LAN.

At least one of a plurality of edge devices (EDs) of the MSN may beconfigured as a gateway ED, with the remaining EDs being designated ascommon EDs. Redundant tunnels may be generated between the gateway EDand each of the common EDs. The redundant tunnels may be redundantInternet protocol (IP) generic routing encapsulation (GRE) tunnels. Thegateway ED may forward IP messages between a core network and a sitenetwork of the MSN. The redundant tunnels generated between the gatewayED and the common EDs may be used to carry the IP messages to provideseamless migration of VMs in the MSN.

According to an example, the gateway ED and one of the common EDs mayimplement an Ethernet virtualization interconnection (EVI) over the MSN.In another example, the gateway ED and one of the common EDs mayimplement an Overlay Transport Virtualization (OTV) technique. In theseexamples, the MSN may be construed as employing EVI and/or OTV. EVI, forinstance, may be used to implement a Layer 2 virtual private network(L2VPN) technique based on an IP core network. A VPN instance may beestablished among different EDs. According to an example, an overlaynetwork may be used to facilitate virtual local area network (VLAN)expansion across geographically dispersed sites. The overlay networkgenerally includes an overlay interface and virtual links to carry Layer2 traffic between sites. For example, the virtual links may be anycommunication channels over a Layer 3 core network. In one example, aphysical communication medium may be virtualized to include multiplecommunication channels such that traffic of one communication channel isseparated from that of a different communication channel (e.g., using asuitable identifier). The virtual link may be a Layer 2 virtual link(e.g., virtual Ethernet link) tunneled through the Layer 3 network usingany suitable protocol (e.g., EVI, GRE, etc.). Layer 2 traffic betweensites may be encapsulated with an IP header (“MAC in IP”) to reach itsdestination via the core network. Traffic may be forwarded in the corenetwork based on the IP header.

According to an example, the VM migration apparatus disclosed herein mayinclude a processor, and a memory storing machine readable instructionsthat when executed by the processor cause the processor to generate aredundant tunnel between a common ED of a plurality of common EDs of aMSN and a gateway ED of the MSN. The machine readable instructions mayfurther cause the processor to configure a gateway media access control(MAC) address and a static route for forwarding an IP message betweenthe common ED and the gateway ED using the redundant tunnel. The machinereadable instructions may further cause the processor to configure thestatic route to include a next hop IP address of the static route as agateway IP address, and an outgoing interface of the static route as theredundant tunnel.

By using the gateway ED of the MSN as a single gateway for the MSN, a VMof the MSN may be seamlessly migrated between different site networks.For example, a host in a core network of the MSN may not perceive themigration of a VM. Further, a migrated VM may not need to update itsaccess gateway address during the migration process.

FIG. 1 illustrates a MSN 100 including a VM migration apparatus 101,according to an example of the present disclosure. According to anexample, the MSN 100 may be an EVI network, an OTV network, etc. Thesimplified configuration of the MSN 100 illustrated in FIG. 1 isprovided for facilitating a description of the operation of the VMmigration apparatus 101. The MSN 100 may include other devicesincluding, such as other servers, EDs, routers, switches, etc.

Referring to FIG. 1, the MSN 100 may generally include site networks 102and 103, a core network 104, and an overlay network 110. The sitenetwork 102 may include a VM1 (e.g., a server 1) and a VM2 (e.g., aserver 2) connected under customer edge (CE) 1. The VM1 and the VM2 maybe connected to the core network 104 through an ED1. In the example ofFIG. 1, the VM1 may include an IP address 10.1.1.10 and a gatewayaddress 10.1.1.1, the VM2 may include an IP address 10.1.1.11 and agateway address 10.1.1.1, and the ED1 may include an IP address10.1.1.1. A site network 103 may include a VM3 connected under CE2. TheVM3 may be connected to the core network 104 through an ED2. In theexample of FIG. 1, the VM3 may include an IP address 10.1.1.12 and agateway address 10.1.1.2, and the ED2 may include an IP address10.1.1.2.

The core network 104 may include a router1 and a host1 connected to therouter1. A MSN link (e.g., EVI link, OTV link, etc.) may be providedbetween ED1 and ED2 that are interconnected via the core network 104. Asdescribed in further detail herein, the ED1 may be designated as agateway ED, and the ED2 may be designated as a common ED. Operation ofthe VM migration apparatus 101 in conjunction with the MSN 100 isdescribed in further detail with reference to FIGS. 2 and 3. Further,each common ED (e.g., ED2) may include an implementation of the VMmigration apparatus 101 for performing the operations described hereinwith reference to FIGS. 1-3.

The overlay network 104 may be a virtual network established between theEDs (e.g., ED1 and ED2) of the site networks 102 and 103. The overlaynetwork 104 may provide a Layer 2 interconnection between the sitenetworks 102 and 103 (and other site networks), may realize extensionsof VLANs among different site networks, may carry Layer 2 data flows ofextended VLANs among the site networks 102 and 103 on a data plane, mayannounce among the site networks 102 and 103, the MAC addressreachability information of all host devices and switching devicesconnected to the EDs (e.g., ED1 and ED2) through an interior gatewayprotocol (IGP) on a control plane, and may interconnect a plurality ofsite networks to form a larger Layer 2 forwarding domain.

FIG. 2 illustrates further details of the VM migration apparatus 101,according to an example of the present disclosure. The VM migrationapparatus 101 may generally include a tunnel generation module 105 togenerate a redundant tunnel (e.g., a redundant IP GRE tunnel) betweenthe common EDs (e.g., the ED2 for the example of FIG. 1) to the gatewayED (e.g., the ED1 for the example of FIG. 1), for carrying an IP messagebetween the common EDs and the gateway ED. The redundant tunnel in theMSN domain may provide the link between the common EDs and the gatewayED. In other words, with respect to the common EDs and the gateway ED,in addition to creating a link tunnel for carrying Ethernet messages,the redundant tunnel that is created may be used to carry IP messages.The redundant tunnel may provide for forwarding of all IP messageexchanges between the site networks 102, 103, and the core network 104,through the gateway ED. The gateway ED may be responsible for releasingroutes of VMs in each of the site networks 102, 103, to the core network104.

An address and route configuration module 106 may configure a gatewayMAC address (i.e., gateway ED MAC address) and a static route forforwarding the IP message using the redundant tunnel between theappropriate common ED and the gateway ED. The gateway MAC address may beused to determine whether to forward the IP message using the redundanttunnel. The configured static route may be used to send the IP messageinto the redundant tunnel when it is needed to forward the IP messagethrough the redundant tunnel. For the static route, the next hop IPaddress of the static route may be a gateway IP address, with theoutgoing interface being the redundant tunnel.

A destination MAC address evaluation module 107 may determine whether adestination MAC address of the IP message originating from the site ofthe common ED and received by a message forwarding module 108 is agateway MAC address.

Based on a determination by the destination MAC address evaluationmodule 107 that the destination MAC address of the IP messageoriginating from the site of the common ED and received by the messageforwarding module 108 is a gateway MAC address, the message forwardingmodule 108 may forward the IP message via the redundant tunnel to thegateway ED according to the static route. The gateway ED may forward theIP message according to a local route table of the gateway ED.Otherwise, based on a determination by the destination MAC addressevaluation module 107 that the destination MAC address of the IP messageis not a gateway MAC address, the message forwarding module 108 mayforward the IP message according to the destination MAC address of theIP message.

The message forwarding module 108 may further receive a free addressresolution protocol (ARP) message sent by a VM migrated to the sitewhere the common ED is located (e.g., see FIGS. 1 and 3, VM1 migratedfrom ED1 to ED2), and send the free ARP message to the gateway ED. Thegateway ED may use the free ARP message to update the local route tablefor the gateway ED. The gateway ED may further forward any IP message,whose destination IP address is the IP address of the VM migrated to thesite where the common ED is located and whose destination MAC address isthe gateway MAC address, from the core network 104 to the common EDthrough the redundant tunnel. When sending the free ARP message to thegateway ED, the message forwarding module 108 may send the free ARPmessage to each of the common EDs so that they can update their localroute tables.

A route update module 109 may update the local route table of therespective common ED (i.e., the common ED for each respectiveimplementation of the VM migration apparatus 101) when the messageforwarding module 108 receives the free ARP message sent by a VMmigrated to the site where the common ED is located. When thedestination MAC address evaluation module 107 determines that thedestination MAC address of the IP message that is received by themessage forwarding module 108 and that originates from the site of thecommon ED is the gateway MAC address, the route update module 109 maydetermine if there is an ARP table entry corresponding to thedestination MAC address. The route update module 109 may furthergenerate a free ARP message whose source IP address and source MACaddress are the source IP address and source MAC address, respectively,of the IP message, if there is a corresponding ARP table entry, and theoutgoing interface of the ARP table entry is a link outgoing interface.The message forwarding module 108 may forward the free ARP messagegenerated by the route update module 109 to the gateway ED. The gatewayED may update the local route table and forward the IP message, whosedestination IP address is the source IP address of the IP message andwhose destination MAC address is the gateway MAC address, from the corenetwork 104 to the common ED through the redundant tunnel.

As described herein, the modules and other elements of the apparatus 101may be machine readable instructions stored on a non-transitory computerreadable medium. In addition, or alternatively, the modules and otherelements of the apparatus 101 may be hardware or a combination ofmachine readable instructions and hardware.

Referring to FIGS. 1-3, FIG. 3 illustrates migration of the VM1 from thesite network 102 to the site network 103. For the example of FIG. 3, thehost1 and the VM1 may access each other through ping. Based on thenetwork configuration by the tunnel generation module 105, the ED1 maybe configured as the gateway of the MSN 100, so that the ED1 becomes thesingle gateway in the MSN 100.

Referring to FIGS. 1 and 3, before migration of the VM1 to the sitenetwork 103 including the common ED2, VM1 may be located in the sitenetwork 102 including the gateway ED1. The gateway ED1 may ascertain theARP table entry corresponding to the VM1. Further, the VM1 may ascertainthe ARP table entry corresponding to the gateway ED1, with the defaultgateway IP address being the IP address 10.1.1.1 of the gateway ED1.

Next, with respect to the VM1 before migration to the site network 103,the gateway ED1 may release a network segment route 10.1.1.1 to the corenetwork 104.

Next, with respect to the VM1 before migration to the site network 103,the router1 may ascertain the network segment route 10.1.1.1, with thenext hop thereof being the gateway ED1.

The process for access of the VM1 by the host1 may include the host1sending a ping message whose source IP address is the IP address of thehost1, and whose destination IP address is the IP address of the VM1.

Next, with respect to the VM1 before migration to the site network 103,the router1 may forward the ping message to the gateway ED1 on which theARP table entry corresponding to VM1 already exists. Further, thegateway ED1 may perform an IP forwarding to forward the ping message tothe VM1.

Next, with respect to the VM1 before migration to the site network 103,the VM1 may return a ping response message whose destination MAC addressis the MAC address of the gateway ED1 (i.e., gateway MAC address), andwhose destination IP address is the IP address of the host1.

Next, with respect to the VM1 before migration to the site network 103,the gateway ED1 may receive the ping response message, and may forwardthe ping response message according to the local route table for thegateway ED1.

Finally, with respect to the VM1 before migration to the site network103, the router1 may perform an IP forwarding after receiving the pingresponse message to forward the ping response message to the host1.

Referring to FIGS. 1 and 3, after migration of the VM1 to the sitenetwork 103, the default gateway IP address of the VM1 remains at10.1.1.1. Further, the gateway ED1 may release a network segment route10.1.1.1 to the core network 104. The router1 in the core network 104may ascertain the route of 10.1.1.1, with the next hop thereof being thegateway ED1. Further, after migration of the VM1 to site network 103,the VM1 may send a free ARP message which is intercepted by the commonED2 and sent to the gateway ED1. The free ARP message may be used by thegateway ED1 to update the ARP table entry and local route tablecorresponding to the migrated VM1. After migration of the VM1 to thesite network 103, if an IP message is sent outside of the site network103 by the common ED2, the ED2 may ascertain the source MAC address ofthe IP message to generate a free ARP message to be sent to the gatewayED1.

Referring to FIGS. 1 and 3, after migration of the VM1 to the sitenetwork 103, the process for access of the VM1 by the host1 through pingmay include the host1 sending a ping message whose source IP address isthe IP address of the host1 and whose destination IP address is the IPaddress of the VM1.

Next, with respect to the VM1 after migration to the site network 103,the router1 may forward the ping message to the gateway ED1. This isbecause, at this stage, the common ED2 has not released a route outsideof the site network 103, and the router1 still ascertains that the nexthop of the network segment route 10.1.1.1 is the gateway ED1.

Next, with respect to the VM1 after migration to the site network 103,the gateway ED1 may receive the ping message and perform a look up inthe local route table to determine the next hop of the route for theping message is the common ED2. Further, the gateway ED1 may determinethat the outgoing interface of the common ED2 is the link outgoinginterface. These determinations by the gateway ED1 may trigger an IPforwarding to encapsulate the ping message in an IP over IP GRE formatto be sent to the common ED2.

Next, with respect to the VM1 after migration to the site network 103,the common ED2 may receive the ping message encapsulated in the IP overIP GRE format. The common ED2 may unencapsulate the ping message fromits IP GRE tunnel, and forward the unencapsulated ping message to theVM1.

Next, with respect to the VM1 after migration to the site network 103,the VM1 may generate and return a ping response message to the commonED2.

Next, with respect to the VM1 after migration to the site network 103,the common ED2 may receive the ping response message, since thedestination MAC address of the ping response message is the gateway MACaddress (i.e., MAC address of the gateway ED1) of the MSN instance(e.g., EVI instance, OTV instance, etc.). A matching policy may redirectthe ping response message to the static route. The ping response messagemay be encapsulated in the IP over IP GRE format according to theconfigured static route. The encapsulated ping response message may beforwarded to the gateway ED1.

Next, with respect to the VM1 after migration to the site network 103,the gateway ED1 may receive the encapsulated ping response message. Thegateway ED1 may unencapsulate the ping message from its IP GRE tunnel,and may further forwards the unencapsulated ping response message to thecore network 104 according to the local route table.

Finally, with respect to the VM1 after migration to the site network103, the router1 may perform an IP forwarding after receiving the pingresponse message to forward the ping response message to the host1.

Generally, when VMs (e.g., the VM1, VM2, or VM3) of a site network(e.g., the site networks 102, 103) are to access a user device (e.g.,the host1) of a core network (e.g., the core network 104), the VMs mayforward an IP message. For the IP message, the destination IP addressmay be the IP address of the user device of the core network, and thedestination MAC address (i.e., next hop MAC address) may be the gatewayMAC address. When the IP message reaches an ED of the site network ofthe forwarding VM, if the ED is the gateway ED (e.g., the ED1 of thesite network 102), then the gateway ED may directly forward the IPmessage to the user device in the core network according to the localroute table of the gateway ED. However, if the ED is a common ED (e.g.,the ED2 of the site network 103), based upon a determination that thedestination MAC address of the IP message is the gateway MAC address,the common ED may forward the IP message to the gateway ED through theredundant tunnel according to the configured static route. Uponreceiving the IP message forwarded through the redundant tunnel, thegateway ED may forward the IP message to the user device in the corenetwork according to the local route table of the gateway ED.

Further, with respect to migration of a VM (e.g., the VM1 of the sitenetwork 102) to a new site network (e.g., to the site network 103), themigrated VM may send a free ARP message. For the new site network, an EDof the new site network may intercept the free ARP message, and updateits local ARP table entries and route table according to the free ARPmessage. If the ED of the new site is a common ED, the ED of the newsite may forward the free ARP message to the gateway ED through anEthernet over IP GRE tunnel to the gateway ED. Upon receiving the freeARP message, the gateway ED may update its local ARP table entries androute table according to the free ARP message. Since the free ARPmessage is forwarded to the gateway ED through the original IP GREtunnel, after the gateway ED updates the corresponding local ARP tableentries according to the free ARP message, the outgoing interface in thelocal ARP table entries may be the link outgoing interface. The free ARPmessage may also be forwarded to the rest of the common EDs through theEthernet over IP GRE tunnels to each of the rest of the common EDs.Accordingly, the rest of the common EDs may update their local ARP tableentries and route tables based on the free ARP message.

For further operations, the gateway ED may receive an IP message sent bya user device (e.g., the host1) in the core network 104. The IP messagemay include a destination IP address as the IP address of a VM and adestination MAC address as the gateway MAC address. For such an IPmessage, the gateway ED may perform an IP forwarding within the MSNaccording to the local route table of the gateway ED to forward the IPmessage to the ED of the new site network through the redundant tunnel.The ED of the new site network may further forward the IP message to theVM of the new site network.

With respect to the free ARP message, in the event the free ARP messagedoes not immediately reach the gateway ED after migration of the VM(e.g., the VM2) to the new site network (e.g., the site network 103),absent receipt of the free ARP message, the gateway ED may not updatethe local ARP table entries and route table in time. Thus, absentreceipt of the free ARP message, for an IP message whose destination IPaddress is the IP address of the VM and whose destination MAC address isthe gateway MAC address to the ED of the new site network, the gatewayED may not forward the IP message originating from the core network 104to the ED of the new site network via the redundant tunnel. Further,such an IP message may not be sent by the new site network to the VM. Toaddress such a situation, when the common ED receives the IP messagewhose destination MAC address is the gateway MAC address from the siteof the common ED, the common ED may ascertain the MAC address of the IPmessage. Further, the common ED may determine whether there is an ARPtable entry corresponding to the ascertained MAC address. Based on adetermination that there is no ARP table entry corresponding to theascertained MAC address, the common ED may ascertain that the devicesending the IP message is not a VM newly migrated to the site network ofthe common ED, and the MAC address may be released. Alternatively, basedon a determination that there is an ARP table entry corresponding to theascertained MAC address and the outgoing interface of the ARP tableentry is the link outgoing interface, the common ED may ascertain thatthe corresponding ARP table entry is ascertained from another sitenetwork. Thus, the common ED may ascertain that the device sending theIP message is a VM newly migrated to the site network of the common ED.In this case, a free ARP message may be generated for the VM newlymigrated to the site network of the common ED. For the free ARP message,the source IP address and source MAC address may be the IP address andMAC address, respectively, of the VM newly migrated to the site networkof the common ED. Further, the free ARP message may be sent to thegateway ED. Upon receipt of the free ARP message, the gateway ED mayupdate its local ARP table entries and route table according to the freeARP message. Further, the gateway ED may forward the IP message from thecore network to the common ED through the redundant tunnel according toits local route table. For the IP message, the destination IP addressmay be the IP address of the VM and the destination MAC address may bethe gateway MAC address. When the common ED forwards the free ARPmessage to the gateway ED, the common ED may also send the free ARPmessage to each of the rest of the common EDs. The remaining common EDsmay thereby update the local ARP table entries and route tables toensure message exchange between the site networks.

FIGS. 4 and 5 respectively illustrate flowcharts of methods 200 and 300for VM migration, corresponding to the example of the VM migrationapparatus 101 whose construction is described in detail above. Themethods 200 and 300 may be implemented on the VM migration apparatus 101shown in FIGS. 1-3 by way of example and not limitation. The methods 200and 300 may be practiced in another apparatus.

Referring to FIG. 4, for the method 200, at block 201, the method mayinclude generating a redundant tunnel between a common ED of a pluralityof common EDs of a MSN and a gateway ED of the MSN. For example,referring to FIGS. 1-3, the method may include generating a redundanttunnel between the common ED2 of the MSN 100 and the gateway ED1. Asdescribed herein, according to an example, the MSN 100 may be an EVInetwork, an OTV network, etc.

At block 202, a gateway MAC address and a static route are configuredfor forwarding an IP message between the common ED (e.g., ED2) and thegateway ED (e.g., ED1) using the redundant tunnel.

Referring to FIG. 5, for the method 300, at block 301, the method mayinclude generating a redundant tunnel between a common ED of a pluralityof common EDs of a MSN and a gateway ED of the MSN.

At block 302, a gateway MAC address and a static route are configuredfor forwarding an IP message between the common ED and the gateway EDusing the redundant tunnel. According to an example, configuring agateway MAC address and a static route for forwarding an IP messagebetween the common ED and the gateway ED using the redundant tunnel mayfurther include configuring the static route to include a next hop IPaddress of the static route as a gateway IP address, and an outgoinginterface of the static route as the redundant tunnel.

At block 303, at the common ED, the IP message is received from a sitenetwork of the common ED. For example, referring to FIGS. 1-3, themethod may include the method may include receiving, at the common ED2,the IP message from the site network 103.

At block 304, a determination is made as to whether a destination MACaddress of the IP message is the gateway MAC address.

At block 305, in response to a determination that the destination MACaddress of the IP message is the gateway MAC address, the method mayinclude forwarding the IP message via the redundant tunnel to thegateway ED (e.g., the gateway ED1) according to the static route.

Other steps may be performed for VM migration. According to an example,the method may include using the gateway ED to forward the IP messageaccording to a local route table of the gateway ED. According to anexample, the method may include migrating the VM (e.g., the VM1) from asite network (e.g., the site network 102) associated with the gateway EDto another site network (e.g., the site network 103) associated with thecommon ED. According to an example, the method may include receiving afree ARP message from the migrated VM, and updating, at the common ED, alocal route table of the common ED. The method may further includeforwarding the free ARP message to the gateway ED, updating, at thegateway ED, a local route table of the gateway ED, and using the updatedlocal route table of the gateway ED to forward the IP message from acore network (e.g., the core network 104) to the common ED. According toan example, the IP message may include a destination IP address as an IPaddress of the VM and a destination MAC address as the gateway MACaddress.

According to an example, the method may include receiving the IP messageincluding a destination MAC address as the gateway MAC address from anetwork site of the common ED (e.g., the common ED2), and determiningwhether there is an ARP table entry corresponding to the destination MACaddress. Based on a determination that there is an ARP table entrycorresponding to the destination MAC address, the method may furtherinclude determining whether an outgoing interface of the ARP table entryis a link outgoing interface. Based on a determination that the outgoinginterface of the ARP table entry is the link outgoing interface, themethod may further include generating a free ARP message whose source IPaddress and source MAC address are the source IP address and source MACaddress, respectively, of the IP message. The method may further includeforwarding the free ARP message to the gateway ED (e.g., the gatewayED1). According to an example, the method may include updating, at thegateway ED, a local route table of the gateway ED, and using the updatedlocal route table of the gateway ED to forward the IP message from acore network to the common ED using the redundant tunnel. According toan example, the method may include forwarding the free ARP message toother common EDs of the plurality of common EDs, and updating, at theother common EDs, respective local route tables of the other common EDs.

According to an example, the method may include migrating the VM from asite network associated with the common ED to another site networkassociated with another common ED of the plurality of common EDs.According to an example, the method may include receiving a free ARPmessage from the migrated VM, and updating, at the another common ED, alocal route table of the another common ED. The method may furtherinclude forwarding the free ARP message to the gateway ED, updating, atthe gateway ED, a local route table of the gateway ED, and using theupdated local route table of the gateway ED to forward the IP messagefrom a core network to the another common ED.

FIG. 6 shows a computer system 400 that may be used with the examplesdescribed herein. The computer system may represent a generic platformthat includes components that may be in a server or another computersystem. The computer system 400 may be used as a platform for theapparatus 101. The computer system 400 may execute, by a processor orother hardware processing circuit, the methods, functions and otherprocesses described herein. These methods, functions and other processesmay be embodied as machine readable instructions stored on a computerreadable medium, which may be non-transitory, such as hardware storagedevices (e.g., RAM (random access memory), ROM (read only memory), EPROM(erasable, programmable ROM), EEPROM (electrically erasable,programmable ROM), hard drives, and flash memory).

The computer system 400 may include a processor 402 that may implementor execute machine readable instructions performing some or all of themethods, functions and other processes described herein. Commands anddata from the processor 402 may be communicated over a communication bus404. The computer system may also include a main memory 406, such as arandom access memory (RAM), where the machine readable instructions anddata for the processor 402 may reside during runtime, and a secondarydata storage 408, which may be non-volatile and stores machine readableinstructions and data. The memory and data storage are examples ofcomputer readable mediums. The memory 406 may include a VM migrationmodule 420 including machine readable instructions residing in thememory 406 during runtime and executed by the processor 402. The VMmigration module 420 may include the modules of the apparatus 101 shownin FIG. 1.

The computer system 400 may include an I/O device 410, such as akeyboard, a mouse, a display, etc. The computer system may include anetwork interface 412 for connecting to a network. Other knownelectronic components may be added or substituted in the computersystem.

What has been described and illustrated herein is an example along withsome of its variations. The terms, descriptions and figures used hereinare set forth by way of illustration only and are not meant aslimitations. Many variations are possible within the spirit and scope ofthe subject matter, which is intended to be defined by the followingclaims and their equivalents in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

What is claimed is:
 1. A method for virtual machine (VM) migration, themethod comprising: transmitting, by a processor, messages between acommon edge device (ED) of a plurality of common EDs of a multi-sitenetwork (MSN) and a gateway ED of the MSN using a tunnel; generating, bythe processor, a redundant tunnel between the common ED of the MSN andthe gateway ED of the MSN; configuring, by the processor, a gatewaymedia access control (MAC) address and a static route for forwarding anInternet protocol (IP) message between the common ED and the gateway EDusing the redundant tunnel; and migrating, by the processor, the VM froma site network associated with the gateway ED to another site networkassociated with the common ED by using the gateway MAC address and thestatic route for forwarding the IP message.
 2. The method according toclaim 1, wherein configuring the gateway MAC address and the staticroute for forwarding the IP message between the common ED and thegateway ED using the redundant tunnel comprises: configuring the staticroute to include a next hop IP address of the static route as a gatewayIP address, and an outgoing interface of the static route as theredundant tunnel.
 3. The method according to claim 1, comprising:receiving, at the common ED, the IP message from the site network of thecommon ED; determining whether a destination MAC address of the IPmessage is the gateway MAC address; and forwarding the IP message viathe redundant tunnel to the gateway ED according to the static route, inresponse to a determination that the destination MAC address of the IPmessage is the gateway MAC address.
 4. The method according to claim 1,comprising: receiving a free address resolution protocol (ARP) messagefrom the migrated VM; and updating, at the common ED, a local routetable of the common ED.
 5. The method according to claim 4, comprising:forwarding the free ARP message to the gateway ED to cause the gatewayED to update a local route table of the gateway ED and use the updatedlocal route table of the gateway ED to forward the IP message from acore network to the common ED.
 6. The method according to claim 5,wherein the IP message includes a destination IP address as an IPaddress of the VM and a destination MAC address as the gateway MACaddress.
 7. The method according to claim 1, comprising: receiving theIP message including a destination MAC address as the gateway MACaddress from a network site of the common ED; determining whether thereis an address resolution protocol (ARP) table entry corresponding to thedestination MAC address; determining whether an outgoing interface ofthe ARP table entry is a link outgoing interface, in response to adetermination that there is an ARP table entry corresponding to thedestination MAC address; generating a free ARP message whose source IPaddress and source MAC address are the source IP address and source MACaddress, respectively, of the IP message, in response to a determinationthat the outgoing interface of the ARP table entry is the link outgoinginterface; and forwarding the free ARP message to the gateway ED.
 8. Themethod according to claim 7, comprising: updating, at the gateway ED, alocal route table of the gateway ED; and using the updated local routetable of the gateway ED to forward the IP message from a core network tothe common ED using the redundant tunnel.
 9. The method according toclaim 7, comprising: forwarding the free ARP message to other common EDsof the plurality of common EDs; and updating, at the other common EDs,respective local route tables of the other common EDs.
 10. The methodaccording to claim 1, comprising: receiving a free ARP message from themigrated VM; updating, at the another common ED, the local route tableof the another common ED; forwarding the free ARP message to the gatewayED; updating, at the gateway ED, the local route table of the gatewayED; and using an updated local route table of the gateway ED to forwardthe IP message from the core network to the another common ED.
 11. Avirtual machine (VM) migration apparatus comprising: a processor; and amemory storing machine readable instructions that when executed by theprocessor cause the processor to: transmit messages between a commonedge device (ED) of a plurality of common EDs of a multi-site network(MSN) and a gateway ED of the MSN using a tunnel; generate a redundanttunnel between the common ED of the MSN and the gateway ED of the MSN;configure a gateway media access control (MAC) address and a staticroute for forwarding an Internet protocol (IP) message between thecommon ED and the gateway ED using the redundant tunnel; and migrate theVM from a site network associated with the gateway ED to another sitenetwork associated with the common ED by using the gateway MAC addressand the static route for forwarding the IP message.
 12. The VM migrationapparatus of claim 11, comprising machine readable instructions to causethe processor to: configure the static route to include a next hop IPaddress of the static route as a gateway IP address, and an outgoinginterface of the static route as the redundant tunnel.
 13. The VMmigration apparatus of claim 12, comprising machine readableinstructions to cause the processor to: receive a free addressresolution protocol (ARP) message from the migrated VM; update, at thecommon ED, a local route table of the common ED; and forward the freeARP message to the gateway ED, to cause the gateway ED update a localroute table of the gateway ED and use the updated local route table ofthe gateway ED to forward the IP message from a core network to thecommon ED.
 14. The VM migration apparatus according to claim 12,comprising machine readable instructions to cause the processor to:receive, at the common ED, the IP message from the site network of thecommon ED; and determine whether a destination MAC address of the IPmessage is the gateway MAC address.
 15. The VM migration apparatusaccording to claim 14, comprising machine readable instructions to causethe processor to: forward the IP message via the redundant tunnel to thegateway ED according to the static route, in response to a determinationthat the destination MAC address of the IP message is the gateway MACaddress.
 16. A non-transitory computer readable medium having storedthereon machine readable instructions to provide virtual machine (VM)migration, the machine readable instructions, when executed, cause aprocessor to: transmit messages between a common edge device (ED) of aplurality of common EDs of a multi-site network (MSN) and a gateway EDof the MSN using a tunnel; generate a redundant tunnel between each ofthe plurality of common ED of the MSN and the gateway ED of the MSN;configure a gateway media access control (MAC) address and a staticroute for forwarding an Internet protocol (IP) message between theplurality of common ED and the gateway ED using the redundant tunnel;receive, at the common ED, the IP message from a site network of thecommon ED; determine whether a destination MAC address of the IP messageis the gateway MAC address; and migrate the VM from the site networkassociated with the gateway ED to another site network associated withthe common ED by using the gateway MAC address and the static route forforwarding the IP message.
 17. The non-transitory computer readablemedium of claim 16, comprising machine readable instructions to causethe processor to: receive a free address resolution protocol (ARP)message from the migrated VM; and update, at the common ED, a localroute table of the common ED.
 18. The non-transitory computer readablemedium of claim 16, comprising machine readable instructions to causethe processor to: forward the IP message via the redundant tunnel to thegateway ED according to the static route, in response to a determinationthat the destination MAC address of the IP message is the gateway MACaddress.
 19. The non-transitory computer readable medium of claim 17,comprising machine readable instructions to cause the processor to:forward the free ARP message to the gateway ED, to cause the gateway EDupdate a local route table of the gateway ED and use the updated localroute table of the gateway ED to forward the IP message from a corenetwork to the common ED.